This invention relates generally to painting. More specifically, the invention relates to additive formulations which improve the transfer efficiency of paint and to methods for the use of the additives.
Spray painting techniques are rapid, and easy to implement, and hence widely employed in many manufacturing processes. However, spray painting generally wastes significant amounts of paint because of overspray, poor adherence and the like. Transfer efficiency is a measure of the amount of paint actually applied to articles being spray painted. Even in the best of processes, 40-45% of the paint is lost, corresponding to a transfer efficiency of 55-65%. Paints are generally quite expensive; hence, any improvement in the transfer efficiency of a painting process will advantageously impact the economics of the process and lessen problems of pollution resultant from inefficiencies in the painting process. It is to be understood that, within the context of this disclosure, the term xe2x80x9cpaintxe2x80x9d is understood to include coating materials colored with pigments or dyes, as well as clear coats, varnishes, sealers, stains and the like.
Particular polymeric additives have been found to improve the transfer efficiency of sprayed paint. U.S. Pat. No. 3,713,872, which is incorporated herein by reference, discloses one such additive comprising an acrylic polymer. U.S. Pat. No. 5,418,283, the disclosure of which is incorporated herein by reference, discloses the use of an ultra high molecular weight acrylic polymer for improving the transfer efficiency of paint. The preferred polymeric materials used in the practice of the present invention are those known in the art as ultra high molecular weight (UHMW) polymers. These polymers typically have a molecular weight of at least 4,000,000, and more preferably a molecular weight in the range of 8,000,000-12,000,000. As disclosed in the ""283 patent, this ultra high molecular weight polymeric material is incorporated into a paint formulation, typically at a concentration of approximately 100-1,000 ppm, and acts to increase the transfer efficiency of the painting process. It should be noted that there is some inherent uncertainty in the measurement of molecular weights of UHMW polymers; therefore, all of the molecular weights given herein are approximate. Molecular weights specified in this disclosure are all measured on the basis of viscosity as detailed in the ""283 patent.
As disclosed in the ""283 patent, solid polymeric material is added to the solvent vehicle of the paint; and in some instances, the polymeric material is added to the paint as a toluene based solution. While the ultra high molecular weight polymers of the ""283 patent do significantly increase the transfer efficiency of paint, as a practical matter, use of the polymeric materials is difficult. The very high molecular weight of the polymer makes the material very difficult to dissolve in most paint formulations, and when the solid polymeric material is added to paints, full dissolution of the material only occurs after several days time. When the UHMW polymer is dissolved in conventional paint solvents such as toluene or xylene, prior to addition to the paint, the resultant paint films have been found to have a poor surface quality. These problems have limited the use of the ultra high molecular weight acrylic polymers as transfer efficiency enhancing agents. Thus, it is necessary to have a method and/or composition which allows ultra high molecular weight, transfer efficiency improving polymers to be incorporated into paints without requiring unduly long dissolution times or adversely affecting the quality of finish of painted articles.
As will be explained in detail hereinbelow, the inventor hereof has found that specific solvent materials readily dissolve ultra high molecular weight, transfer-efficiency-improving polymers, so as to permit their ready incorporation into paint compositions; additionally, this group of additive solutions do not adversely affect the quality of painted surfaces produced therefrom.
There is disclosed herein an additive for improving the transfer efficiency of paint. The additive is comprised of a polymer having a molecular weight of at least 4,000,000 and a solvent for the polymer. The solvent is selected from the group consisting of glycol ethers, halogenated aromatic materials, and combinations thereof. In a particular group of embodiments, the polymer has a molecular weight in the range of 8,000,000-12,000,000, and in a specifically preferred embodiment, the polymer is an acrylic polymer.
The glycol ether may comprise a monoalkyl ether, and in specific embodiments, the monoalkyl ether is a C1-C4 alkyl ether. In other embodiments, the glycol ether is an ester of a glycol ether, and one particularly preferred glycol ether ester comprises ethylene glycol monoethyl ether acetate. In certain embodiments, the halogenated aromatic compound is a chlorofluoro aromatic compound such as parachlorobenzotrifluoride. In other embodiments, the halogenated aromatic compound is a chlorotoluene, while in yet other embodiments the halogenated aromatic compound is a benzotrifluoride.
Also disclosed herein are methods for improving the transfer efficiency of paint through the use of the additive of the present invention. In a typical application, the additive is present in the paint in an amount sufficient to provide a concentration in the range of 50-300 ppm of the ultra high molecular weight polymer in the paint.